1. Field of the Invention
The present invention relates generally to an improvement of optical distance measuring method and an optical distance meter for measuring distance to an object by utilizing light beam irradiated from the distance meter to an object. The present invention particularly concerns an improvement in optical distance measuring method an optical distance meter which uses infrared light beam and measures distance by measuring intensity of light reflected from the object.
2. Description of the Prior Art
Hitherto, as method of measuring distance by optical method, there are a first method of transmitting an infrared light beam onto the object and measuring intensity of light beam reflected thereby and a second method of transmitting an infrared light beam onto the object to make triangulation.
The above-mentioned first method distance measuring method is advantageous since the apparatus does not need expensive array of photoelectric elements nor need a long base line length. But the above-mentioned type distance measuring system has such a problem as necessitating a constant intensity of the transmitted light beam and also large intensity of the light beam to enable measurement of a long distance with a high accuracy. This is because the system is to measure the intensity of the reflected light which is produced by transmitting a light beam of an accurately controlled constant intensity. Therefore, in order to achieve such accurate controlling of the transmitted light beam, a great care must be taken in selection of the light transmission part and the power source and the shape.
Accordingly, in order to enable measurement of a considerable distance with the light beam of a small energy, that is, in order to improve efficiency of the light receiving, recent improvement proposes use of pulse-modulation of the transmitted infrared light beam with a predetermined modulation frequency and to receive the pulse-modulated infrared light beam with a receiver having a resonator which resonate to the predetermined modulation frequency.
Though using the above-mentioned system, yet there is a difficulty that the resonance frequency is likely to deviate due to divergence of electric constants thereof and thermal fluctuation of them, and that the resonance frequency must be accurately tuned in order to achieve a receiving signal at a high sensitivity.
Accordingly, further improvements to dissolve the above-mentioned problems have been strongly expected.